It has been hitherto known in the rubber industry that when a rubber composition containing a filler, such as carbon black, is produced, a rubber wet masterbatch is used to improve the workability of the composition and the dispersibility of the filler. This situation is a situation of mixing the filler and a dispersing solvent beforehand with each other at a predetermined ratio therebetween, dispersing the filler into the dispersing solvent by a mechanical force to yield a filler-containing slurry solution, mixing this slurry solution with a rubber latex solution in a liquid phase, adding a solidifier such as an acid into the mixture to solidify the mixture, and then collecting and drying the solidified mixture. In the case of using the rubber wet masterbatch, a rubber composition is obtained which is better in filler dispersibility therein and rubber properties such as workability arid reinforceability than in the case of using any dry masterbatch obtained by mixing a filler and a rubber with each other in a solid phase. The use of such a rubber composition as a raw material makes it possible to produce, for example, a pneumatic tire and other rubber products that have a decreased rolling resistance and an excellent fatigue resistance.
Apart from the above description, about a vulcanized rubber for tires, a rubber composition may be used which is obtained by mixing two or more rubber wet masterbatches with each other.
As a technique of using two or more rubber wet masterbatches as a raw material, Patent Document 1 listed below describes a technique of wet-mixing a rubber wet masterbatch (A) with a rubber wet masterbatch (B) different in composition from the rubber wet masterbatch (A), and next kneading and drying the mixture.